Method of sintering



Oct. 30, 1956 M, L. COVER METHOD OF SINTERING 3 Sheets-Sheet 1 FiledApril 2'7, 1951 m R m MW m m W Z A W k NN\ 110w MM D 323225 2Q m g l MQ\ Oct. 30, 1956 M. L. COVER METHOD OF SINTERING -3 Sheets-Sheet 2 FiledApril 27, 1951 r H W. m W v W m c w r m r 4 A W 7 k A M Y om B mm v &M\\ wrfi i Oct. 30, 1956 M. COVER ,7 0

METHOD OF SINTERING Filed April 27, 1951 s Shets-Sheet 3 U INVENTOR.

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United States PatentO METHOD OF SINTERING Martin L. Cover, Allen Park,Mich.

Application April 27, 1951, Serial No. 223,375

2 Claims. (Cl. 755) This invention relates to a method and apparatus formaking sinter.

In blast furnace operation it is common to use material called sinter asa part of the furnace charge. One ingredient of sinter is finely dividedore, sometimes ground up in order to concentrate the valuable portion.Other ingredients include recovered flue dust, recovered fines, powderedcoke and mill scale. This fine material cannot be fed directly to thefurnace since it would blow out and reduce the efiiciency of thefurnace.

These ingredients, all in relatively fine condition, are mixed togetherwith a suitable amount of moisture and distributed on moving beds calledpallets. The top of the distributed mixture is ignited and air is pulledthrough the bed from top to bottom to stimulate the burning action andcarry it through the material. This burning action tends to cake-up thematerial after which it is broken up into chunks 3" in diameter andlarger, and fed to the stock pile for the blast furnace. It is importantthat the resulting sinter have a certain structural strength so that itwill not slack-out or crush in the handling operations and in the blastfurnace.

It is an object of the present invention to provide a sintering appatuswhich eliminates dust hoppers. Suction creating means, called windboxes, draw air through the burning beds. Previously it has beennecessary to provide hoppers to catch fines dropping from the bed or pIn the present apparatus an enclosed controlled wind passage will carryescaping fines to a dust catcher. A similar treatment at the loading anddischarge end of the pallet lines carries all recovered, dust and finedroppings to a collecting source where itis added to the flow ofmaterial to the sintering beds.

Another object of the inventionv is the introduction of a filter cakeinto the mix to retain moisture at the lower portion of the bed'thuspreventing the material from drying out before burning.

the moist material issues to the required pug mill.

to prevent drying prior to burning, a better quality sinter,

a greater q'uantity of sinter, an apparatus subject to' accurate controlfor such production, and an apparatus for producing sinter in the propersize for use.

.Drawings accompany the description to illustrate the apparatus and toassist'in the disclosure of t-hesteps of, l the method. The variousviews thereof may be described 'briefly. as follows:

' Fig. 1, a' diagrammatic elevation of the sintering machine.

.. Fig. 2, a sectional view on line 2, 2of ig. .1. H

In this connection fine ore such as Taconiteand finely divided fuel areIi-mixed into the recovery lines of the system and dispatched to a.settler and thence. to the filter from which "ice Fig. 3, a sectionalview on line 3-3 of Fig. 1.

Fig. 4, a diagrammatic plan of the apparatus.

Fig. 5, a rear enlarged view of the discharge end of the sinter machine.

Fig. 6, an elevation of the discharge end of the sinter machine.

The sintering system to be described is a variation of that accomplishedwith a Dwight-Lloyd sintering machine. As shown in the drawings a seriesof driven pallets are illustrated diagrammatically at 20 moving in aclosed circuit. In the usual sequence, these pallets in the uppertraverse are loaded, fired, and dumped. The charge, in the present case,is related to the method of operation in which recoverable dust andfines are mixed with fine ore and fine fuel (breeze) and recovered in asettling tank. As sludge this material is sent to a filter and removedtherefrom as moist filter cake. The filter cake plus the usual charge offlue dust, ore, scale, and fine coke is then sent to a plug mill andmixed before being loaded on the moving pallets.

A plurality of wind boxes 22, in this case twelve, underlie the palletseach with a duct 26 leading down to a wind manifold 24 which extendsbelow the sintering bed to a dry dust catcher 28. The lower traverse ofthe pallets travels just above another series of supplemental windcollector boxes 30 each connected to the manifold 24 by a short duct 32in which is mounted a control damper 34. The bottom wall of the manifold24 is sloped down toward the dry dust catcher about 10 to 15".

At the dumping end of the sintering traverse is a bond 40 extending overan area equal to about the last 5 Wind boxes. An end chute hood 42 topsan end chute 46 overlying the grizzlies 50 which are spaced bars uponwhich the dislodged sinter falls asit passes to a cooling conveyor 52.An air pipe 44 connects the hood 42 to manifold 24 to create reducedpressure in the hood.

Below the grizzlies 50 is a hot fines bin 54 which receives hot finesfrom the grizzlies 50 and discharges it to a conveyor later to bedescribed. A rotating table 56 removes the fines from the bin anddeposits them on the' belt.

A dust recovery cap 60 is positioned at the point of loading from thehot fines bin and connected by a conduit 62 to the end of manifold 24 tocreate a low pressure area in this locality where dust might develop.

' At the loading end of the sintering machine, two hoppers 66 and 68extend beyond the twelve wind boxes to collect falling particles anddust at this loading area. A damper control may be used to preventexcessive draft here. A third hopper 70 at the end of the manifold ispositioned to receive fine ore and breeze (fine coke) from supply binsas will be later described.

The manifold 24 terminates in the dry dust catcher 28 which collectscoarse material that will not carry up with the moving air. A large windpipe 72 leads to a combined washer and settling tank 74 described in myPatent No. 2,539,992 issued January 30, 1951. Air is pulled through thetank 74 to a pipe 76 by a vacuum fan 78 capable of handling for thepresent disclosure about I dinary sinter forming materials such as fluedust, ore scale,

:the yard. Material of suitable size willpass through the screening unitto a shuttle conveyor 102 which fills bins 104with sinter mix.

A conveyor 106 below bins 104 carries sinter material vfrom the bins toa transverse conveyor 108 which in turn carries the material to a longascending conveyor 110 leading to a pug mill. A short conveyor 111deposits ma- .terial from the dry dust-catcher into the conveyor 106 atthe beginning of its upper run toward the bins '104. Meanwhile sludgefrom the washer and settler'has been pumped to a filter 112 from whichit emerges on to a conveyor .113 which dumps the moist filter cake intocsonveyor 103 leading to conveyor 110 and the pug mill.

.A diverting conveyor 113A can convey filter cake to 'the yard ifexcessive in quantity or if plant is down.

But bins 93 and 94 containing fine ore and powdered fuel are serviced bya separate conveyor 114, 115, 116, 117 which carry material from thesebins to a hopper 70 at the end of manifold 24. Thus powdered ore andpowdered fuel are introduced into the products of the washer 74 andfilter 112 to provide a moist filter cake having about 26 to 30%moisture remaining. A feeder to control the amount of fines introducedinto the air stream is provided with the hopper 70. A rotating cylinderwith radial blades at the bottom opening will move the material outevenly. My copending application Serial No. 181,654 filed August 26,1950, now abandoned, shows such a device.

From the pug mill the material is carried by a conveyor 120 to aswinging spout 125 where it is distributed to the pallets 20 as'theystart their upper traverse. This swinging spout is described in myPatent 2,422,470 issued June 17, 1947. Adjacent the swinging spout is anignition device 127 as disclosed in my Patent No. 2,375,895 issued May15, 1945.

If only one pug mill is used and no fluifers after the filter cake isintroduced a large part of the filter cake will form balls which greatlyaid in the sintering process.

On the Dwight Lloyd sintering machine the sinter mix is ignited on thetop and air is pulled by vacuum down through the sinter bed. For maximumquantity and highest quality of sinter production the total sinter mixmust contain around 9% to 12% moisture. It must contain the correctamount of carbon and the bed must be as porous as possible. In order toobtain these highest results a 28 H2O vacuum and about 13" deep bedshould be used. A higher vacuum and a deeper bed should give stillbetter results but the hot products of combustion have a tendency to dryout the lower part of the bed. The 28" vacuum and the 13 bed, I havefound, gives the optimum results with materials I use.

The halls of fine material formed from the filter cake contains a ratherhigh amount of moisture. A rather large proportion of these balls willaccumulate at the lower part of the bed and help to keep the moisture inthe mix between the 9% and 12% limits, if the 28" vacuum and 13" bed areused.

When extra pug mills or fluffers are used they tend to break up theseballs. The moisture is then not carried to the lower part of the bed andthe fine materials cause the bed to tighten up and lose its porosity.This has a tendency to reduce both the quantity and the quality of thesinter made.

In a plant where belt scrapers, junction boxes, filter scrapers,filtrate removers, swinging spout, pug mill and belt speeds and widthsare properly engineered the total mix may contain up to 50% of the 26%to 30% moisture filter cake and sinter of the very highest quality canbe made.

The amount of this high moisture filter cake that can be used in thisplant is limited only by the amount of moisture and carbon itcontainsthat can be neutralized by the hot return fines. I use from 25%to 30% of the total mix from these returns, and have them at a brightred temperature. The temperature and amount of these returns arecontrolled by the use of grizzly packs" that I have developed and whichcan be changed with little or no delay in the sintering operation.

The ordinary 'swin'gingspoufwill nothandle the high percentage of verywet filter cake. I have developed a swinging spout as disclosed in'iriyPatntfNo. 2,422,470 that keeps the sinter bed fiufiy and porous, doesnot break up the balls of fine materials and does not require any handpounding. It would easily "handle 1800 tons of 26% to 30% moisturefilter cake in 24 hours if the returns neutralize the moisture andcarbon in it so that the total mix will contain the right percentage ofmoisture and carbon. 1

In this layout I vuse a table feeder for the very fine ore such asTaconite and one for the fuel so that they are mixed in the correctproportions. This mixture is then fed into the sloping wind main withjust enough air leaking in to keep down the dust. Insidethe main thewind thoroughly mixes the fine ore and the fuel.

In the usual layout, the fan is designed to handle 9,000 cu. ft. :of airper minute per wind box. It is pretty well established that this is thecorrect amount of air to get best results. p

In order to take care of the air that leaks in at the various points, Ihave increased the fan size so that it will handle over 10,000 cu. ft.of air 'per minute per wind box.

The following shows the unusual results that can be obtained with mylayout for handling fine materials and my method of operation. 'On a 12wind box machine the following results can be obtainedin 24 hours opera-'tion.

Percent Mois- Net Tons ture Content (a) Material:

Blast furnace catcher dust 12 Blast furnace filter cake 30 250 Blastfurnace 0113-. 12 600 Taconite ore in filter cake 30 1, 400 Sinterproduced 1, 630

Quality Excellent.

(b) B. F. Catcher dust 12 800 B. F. Filter cake"-.. 3O 1, 700 B. F. Ore00 Sinter produced 1, 700

Quality of sinter excellent if carbon and moisture can be controlled bythe return fines.

If driedout filter cake (10% moisture) is used:

13. F. Catcher dust.-. 12 500 B. F. washer dust 600 Sinter produced 850Quality poor.

The dry dust catcher 28 is of very simple design. No attempt is made toremove any of the very fine materials as they can be handled to a muchbetter advantage in the filter cake. The sand blast action of air variesapproximately in proportion to the square of the wind velocity. Eddycurrents increase this wear and cause vacuum loss. For this reason toono whirling action and comparative low velocities of air are used inthis dust catcher. r

A combined washer and thickener 74 follows the dust catcher. The washerthoroughly cleans and drys the wind so that the life of the fan bladesis indefinite and the surrounding air is not polluted with dust andfumes.

The thickener has no moving parts and does not take up an excessiveamountof space.

The plant as thus layed out is free from the dust that originates fromthe sinter. The surrounding air is also free from dust produced in thesinter plant.

About twice as much very fine material can be handled than is possiblewith the usual plant layout and design.

A strong sinter free from Fayolite and at a very high production rate ismade possible.

Referring to the drawings, in Figs. 5 and 6 I have shown the dischargeend of the sintering conveyor diagrammatically but in sufficient detailto disclose a method of tuming the sinter cake as it falls from theendless conveyor system. The reason for this turning is that a certainamount of sinter must be returned as hot fines to the 'sinter mix. It isbest to return that part of the sinter cake which has the leaststructural strength and the most potential with relation to the dustmaking characteristics.

Now when the cake is dumped off right side up the fines on the top andthe weakest material goes to the sinter stock yard. I propose to turnthe cake as it falls so the top side hits the grizzly bars. Thus most ofthe fines will drop through the grizzlies and go into the hot fines bin.Also since returns larger than are detrimental, they can be screenedout. Previously it was necessary to use larger returns to get enough.With the present system enough hot fines of A" and smaller areobtainable to avoid use of the larger returns. Another advantage of thisturning operation is that the hot sinter lands on top where it will coolmore readily as it passes to the stock yard.

In Fig. 5 a block of sinter S usually leaves the pallet at 30 to 45. Iprovide a plate 140 between walls 141 and 142 to guide the sinter cakedownward. This plate 140 is adjustable to difierent thicknesses of cake.

Guide bars 144 direct the cake almost straight down where a cornerstrikes steps or bumper blocks 146 which catch the cake and cause it toturn over before it hits the grizzlies 150. With this arrangementgrizzlies 150 with 3" spacing may be used to remove large chunks and alower set of grizzlies 152 with /2" or slight larger spacing may be usedto permit only fine materials to pass into the hot fines bin. 1

What I claim is:

1. A method in connection with the use of a sinter-ing apparatus whichcomprises collecting dust and recoverable particles from all parts ofsaid machine in a moving stream of air, introducing into said stream ameasured quantity of fine ore and fine fuel, removing coarse particlesfrom said stream in dry condition, washing the remaining particles fromsaid stream with water, removing the water from said recovered particlesto leave a material containing 26 to 30% moisture, and introducing saidmoist material into a sinter bed adjacent the lower portion thereof inballed dispersed condition.

2. A method in connection with the use of a sintering apparatus whichcomprises moving pallets in a continuous motion in loaded and unloadedcondition, drawing air into a moving stream from loaded pallets, emptypallets, and from the loading end and discharge end of said machine,introducing into said stream a measured quantity of fine ore and finefuel, washing the collected particles from said stream with water,removing the water from said collected particles to leave a materialcontaining 26 to 30% moisture, and introducing said moist material intoa sinter bed adjacent the lower portion thereof in balled dispersedcondition.

References Cited in the file of this patent UNITED STATES PATENTS1,303,411 Swart et al. May 13, 1919 1,305,817 McAfee June 3, 19191,312,218 Vogel Aug. 5, 1919 1,738,940 Boynton Dec. 10, 1929 1,780,833McGurty Nov. 4, 1930 1,826,183 Lehrecke Oct. 6, 1931 2,052,329 WendebornAug. 25, 1936 2,364,586 Morgan Dec. 5, 1944 2,391,588 Naratil Dec. 25,1945 2,412,104 Stewart Dec. 3, 1946 2,519,179 Duncan Aug. 15, 19502,596,132 De Vaney May 13, 1952 FOREIGN PATENTS 502,416 Great BritainMar. 16, 1939 OTHER REFERENCES The Iron Age, March 2, 1944, pp. 46-49.

1. A METHOD IN CONNECTION WITH THE USE OF A SINTERING APPARATUS WHICHCOMPRISES COLLECTING DUST AND RECOVERABLE PARTICLES FROM ALL PARTS OFSAID MACHING IN A MOVING STREAM OF AIR, INTRODUCING INTO SAID STREAM AMEASURED QUANTITY OF FINE ORE AND FINE FUEL, REMOVING COARSE PARTICLESFROM SAID STREAM IN DRY CONDITION, WASHING THE REMAINGING PARTICLES FROMSAID STREAM WITH WATER, REMOVING THE WATER FROM SAID RECOVERED PARTICLESTO LEAVE A MATERIAL CONTAINING 26 TO 30% MOISTURE, AND INTRODUCING SAIDMOIST MATERIAL INTO A SINTER BED ADJACENT THE LOWER PORTION THEREOF INBALLED DISPERSED CONDITION.